1. Field of the Invention
The present invention relates to a semiconductor device with a multilayer wiring structure.
2. Description of Related Art
A so-called multilayer wiring structure, in which a plurality of wiring layers are laminated on a semiconductor substrate, is employed in a semiconductor device, such as an LSI of a high integration.
In semiconductor devices employing such a multilayer wiring structure, in place of Al (aluminum) which has been conventionally used as a wiring material, application of Cu (copper), which is higher in conductivity is being studied in order to reduce wiring resistance.
In a multilayer wiring structure using a Cu wiring material, a first insulating film formed of SiO2 (silicon oxide) is laminated onto a semiconductor substrate formed of Si (silicon). A microscopic wiring groove corresponding to a predetermined wiring pattern is formed in a surface layer portion of the first insulating film. In the wiring groove, a first Cu wire is embedded via a Ta (tantalum-based) barrier film for preventing diffusion of Cu into the insulating film.
A second insulating film formed of SiO2 is laminated on the first insulating film. A microscopic wiring groove corresponding to a predetermined wiring pattern is formed in the second insulating film. Furthermore, in the second insulating film, a via hole is penetratingly formed at a portion where the wiring groove opposes the first Cu wire. A second Cu wire is embedded together in the wiring groove and the via hole via a Ta (tantalum-based) barrier film for preventing diffusion of Cu into the insulating film. The second Cu wire is thereby electrically connected to the first Cu wire.
An insulating film formed of SiO2 and a surface protective film formed of SiN (silicon nitride) are formed on the second insulating film. A penetrating hole for exposing a portion of the second Cu wire for electrical connection to an external portion is formed at portions of the surface protective film that oppose the second Cu wire.
However, because Cu has a property of corroding due to oxidation, when the portion of the second Cu wire is left exposed from the penetrating hole, the exposed portion of the second Cu wire becomes corroded and reliability of electrical connection with the external portion may degrade. Thus, in the conventional semiconductor device, the exposed portion of the second Cu wire is covered by an electrode pad formed of Al (aluminum) having excellent corrosion resistance.
More specifically, a third insulating film formed of SiO2 is formed on the second insulating film. A connection opening that exposes a portion of the second Cu wire is formed at a portion of the third insulating film that opposes the second Cu wire. An electrode pad of a predetermined pattern made of Al is formed so as to coat an interior of the connection opening and a peripheral portion of the connection opening on a surface of the third insulating film. The electrode pad is electrically connected to the second Cu wire via the connection opening.
A surface protective film formed of SiN is formed on the third insulating film on which the electrode pad is formed. In the surface protective film, a pad opening is formed for exposing the electrode pad.
In order to form the electrode pad made of Al, after forming the second Cu wire in a process for manufacturing the semiconductor device, following steps must be carried out additionally, such as: forming the third insulating film→forming the connection opening→forming the electrode pad→forming the surface protective film→forming the pad opening consequently, the increase of the number of manufacturing steps leads to increase of manufacturing cost.